Lleyton Hewitt's [Images] indomitable spirit saw him through to the fourth round of the U.S. Open on Sunday.

The Australian third seed secured a 6-3, 3-6, 6-7, 6-2, 7-5 victory over heavy-serving American Taylor Dent in a third-round thriller on Arthur Ashe Court.

Dent, beaten by Hewitt in the Wimbledon [Images] fourth round this year, refused to lie down and saved three match points before the Australian cut to the quick and finished him off with an ace.

"It was an extremely tough match," admitted Hewitt, who lost their last hardcourt encounter in his hometown of Adelaide this year. "I really had to earn it."

The 2001 champion, who is in line to meet his nemesis Roger Federer [Images] in the semi-finals, will play either David Ferrer of Spain or Dominik Hrbaty of Slovakia in the fourth round.

Russian ninth seed Nadia Petrova reached the women's quarter-finals for the second consecutive year with a 7-6, 7-5 victory over temperamental Czech 16-year-old Nicole Vaidisova.

Petrova, who has never won a tour title, used all her experience to edge out the teenager and Vaidisova vented her frustration by hurling her racket and then her drink across the court at one stage.

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